As described in Japanese Patent Application Publication No. 2007-194823, the recent videoconference systems detect a state of a network by exchanging information regarding a communication packet loss, a communication delay time, etc., through a server that relays image data between or among the terminals. Based on the detected network state, the recent videoconference systems change a resolution or a frame rate of image data for transmission, thus allowing image data to be transmitted in realtime even when the network is unstable.
FIG. 5 illustrates a configuration of a background videoconference system 100. The background videoconference system 100 includes a camera 110A, a display 112A, and a communication terminal 114A, which are provided at a first location site (“first site”). The background videoconference system 100 further includes a camera 110B, a display 112B, and a communication terminal 114B, which are provided at a second location site (“second site”). The background videoconference system 110 further includes a server 130 connected to the terminals 114A and 114B through a network 140 such that the server 130 relays data between the terminals 114A and 114B. The terminals 114A and 114B each include an encoder 116, a decoder 118, and a network state detector 120.
Referring to FIGS. 5 and 6, operation of transmitting image data from the terminal 114A to the terminal 114B, performed by the background videoconference system 100 of FIG. 5, is explained.
At S101, the network state detector 120A of the terminal 114A exchanges network state information D12 regarding an available communication band, a packet loss rate, etc. of the network 140 with the server 130 to detect the state of the network 140.
At S102, the network state detector 120A calculates a transmission data size that is suitable to the detected network state, and transmits information D13 regarding the calculated transmission data size to the encoder 116A.
At S103, the encoder 116A encodes image data D11 captured by the camera 110A by adjusting image parameters such that the encoded image data D14 has the suitable transmission data size. For example, the image data D11 is encoded such that the encoded image data D14 has a data size that is equal to or less than the suitable transmission data size.
At S104, the encoder 116A transmits the encoded image data D14 to the server 130 through the network 140.
At S105, the server 130 relays the encoded image data D14 received from the encoder 116A to the terminal 114B through the network 140, as relay image data D15.
At S106, the decoder 118B of the terminal 114B decodes the image data D15 into decoded image data D16.
At S107, the display 112B at the second site displays an image based on the decoded image data D16.
By repeating operation of FIG. 6, image data is exchanged between the remotely located sites to carry out videoconference. Further, the background videoconference system 100 adjusts image quality of the image data for transmission based on the network state, thus suppressing degradation in sound quality or delay in data transmission that may be otherwise caused when the network is unstable.